Rectangular nanosheet fabrication

Abstract

Exemplary embodiments provide methods for fabricating a nanosheet structure suitable for field-effect transistor (FET) fabrication. Aspects of exemplary embodiment include selecting an active material that will serve as a channel material in the nanosheet structure, a substrate suitable for epitaxial growth of the active material, and a sacrificial material to be used during fabrication of the nanosheet structure; growing a stack of alternating layers of active and sacrificial materials over the substrate; and selectively etching the sacrificial material, wherein due to the properties of the sacrificial material, the selective etch results in remaining layers of active material having an aspect ratio greater than 1 and substantially a same thickness and atomic smoothness along the entire cross-sectional width of each active material layer perpendicular to current flow.

We claim: 
     
         1 . A method for fabricating a rectangular nanosheet structure, comprising:
 selecting an active material that will serve as a channel material in the nanosheet structure, a substrate suitable for epitaxial growth of the active material, and a sacrificial material to be used during fabrication of the nanosheet structure;   growing a stack of alternating layers of active and sacrificial materials over the substrate; and   selectively etching the sacrificial material, wherein due to properties of the sacrificial material, the selective etch results in remaining layers of active material having an aspect ratio greater than 1 and substantially a same thickness and atomic smoothness along the entire cross-sectional width of each active material layer perpendicular to current flow.   
     
     
         2 . The method of  claim 1 , wherein the sacrificial material has properties including: a close lattice match to the active material; admits high quality growth on the active material and vice versa; and a chemical dissimilarity from the active material sufficient to enable highly selective etches. 
     
     
         3 . The method of  claim 2 , wherein sufficient chemical dissimilarity is achieved by the active material comprising Group IV atoms, and the sacrificial material comprising Group II-VI or III-V atoms. 
     
     
         4 . The method of  claim 2 , wherein sufficient chemical dissimilarity is achieved by the active material comprising fully covalent Group IV materials, and the sacrificial material having ionic or polar character in their bonds. 
     
     
         5 . The method of  claim 1 , wherein the active material comprises at least one of silicon (Si); silicon (Si) and germanium (Ge); germanium (Ge); or a III-V or II-VI material. 
     
     
         6 . The method of  claim 5 , wherein the sacrificial material comprises at least one of Zinc sulfide (ZnS), zinc selenide (ZnSe), beryllium sulfide (BeS), or beryllium selenide (BeSe), gallium phosphide (GaP), aluminum phosphide (AlP), gallium arsenide (GaAs), aluminum arsenide (AlAs), gallium phosphide arsenide alloy (GaPxAs1−x), aluminum phosphide arsenide alloy (AlPxAs1−x), or a rare earth oxide including neodymium oxide (Nd2O3), gadolinium oxide (Gd2O3), samarium oxide (Sm2O3), dysprosium oxide (Dy2O3), erbium oxide (Er2O3), or europium oxide (Eu2O3). 
     
     
         7 . The method of  claim 1 , wherein the aspect ratio of the active material is significantly greater than 2. 
     
     
         8 . The method of  claim 1 , wherein the aspect ratio the active material is greater than or equal to 5. 
     
     
         9 . The method of  claim 1 , wherein the aspect ratio the active material is greater than or equal to 10. 
     
     
         10 . The method of  claim 1 , wherein the selective etch has a selectivity greater than 5:1. 
     
     
         11 . The method of  claim 1 , wherein the layers of active material have a thickness variation in the range of less than or equal to 10% from a nominal thickness. 
     
     
         12 . The method of  claim 1 , wherein the layers and of active material have a thickness variation in the range of less than or equal to 5% from a nominal thickness. 
     
     
         13 . The method of  claim 1 , further comprising: etching parallel trenches through the sacrificial material and the active material to at least a level as low as the substrate, leaving behind parallel nanosheet stacks comprising layers of the active and sacrificial materials. 
     
     
         14 . The method of  claim 13 , wherein the width of each of the active nanosheets may be in at least one range of 40-80 nm, 20-40 nm, and 5-20 nm. 
     
     
         15 . The method of  claim 13 , further comprising: depositing spacers and a dummy source/drain fill orthogonal to the direction of the nanosheet stacks. 
     
     
         16 . The method of  claim 15 , wherein the active nanosheets are surrounded on four sides by a dielectric and gate material resulting in a gate-all-around-structure. 
     
     
         17 . The method of  claim 15 , wherein the active nanosheets are surrounded on three sides by a dielectric and gate material resulting in a tri-gate structure. 
     
     
         18 . A field effect transistor (FET), comprising:
 a nanosheet structure of stacked and spaced nanosheet layers, wherein each layer comprises of one or more active nanosheets, each active nanosheet having a high aspect ratio and substantially a same thickness and atomic smoothness along the entire cross-sectional width of a nanosheet perpendicular to current flow; and   wherein the nanosheet structure results from removing sacrificial nanosheet material selective to the active nanosheet material by a selective etch, wherein due to properties of the sacrificial nanosheet material, the selective etch results in the nanosheet layers having an aspect ratio greater than 1 and substantially a same thickness and atomic smoothness along the entire cross-sectional width of each of the active nanosheets perpendicular to current flow.   
     
     
         19 . The FET of  claim 18 , wherein the sacrificial material has properties including: a close lattice match to the active material; admits high quality growth on the active material and vice versa; and a chemical dissimilarity from the active material sufficient to enable highly selective etches. 
     
     
         20 . The FET of  claim 19 , wherein sufficient chemical dissimilarity is achieved by the active material comprising Group IV atoms, and the sacrificial material comprising Group II-VI or III-V atoms. 
     
     
         21 . The FET of  claim 19 , wherein sufficient chemical dissimilarity is achieved by the active material comprising fully covalent Group IV materials, and the sacrificial material having ionic or polar character in their bonds. 
     
     
         22 . The FET of  claim 18 , wherein the active material comprises at least one of silicon (Si); silicon (Si) and germanium (Ge); germanium (Ge); or a III-V or II-VI material. 
     
     
         23 . The FET of  claim 21 , wherein the sacrificial material comprises at least one of: Zinc sulfide (ZnS), zinc selenide (ZnSe), beryllium sulfide (BeS), or beryllium selenide (BeSe), gallium phosphide (GaP), aluminum phosphide (AlP), gallium arsenide (GaAs), aluminum arsenide (AlAs), gallium phosphide arsenide alloy (GaP x As 131 x ), aluminum phosphide arsenide alloy (AlP x As 1-x ), or a rare earth oxide including neodymium oxide (Nd 2 O 3 ), gadolinium oxide (Gd 2 O 3 ), samarium oxide (Sm 2 O 3 ), dysprosium oxide (Dy 2 O 3 ), erbium oxide (Er 2 O 3 ), or europium oxide (Eu 2 O 3 ). 
     
     
         24 . The FET of  claim 18 , wherein the aspect ratio of the active material is significantly greater than 2. 
     
     
         25 . The FET of  claim 18 , wherein the aspect ratio the active material is greater than or equal to 5. 
     
     
         26 . The FET of  claim 18 , wherein the aspect ratio the active material is greater than or equal to 10. 
     
     
         27 . The FET of  claim 18 , wherein the selective etch has a selectivity greater than 5:1. 
     
     
         28 . The FET of  claim 18 , wherein a width of each of the active nanosheets may be in at least one range of 40-80 nm, 20-40 nm, and 5-20 nm.